The present invention relates to a fiber optic pH probe which is suitable to be implanted in the body of a human or other animal for physiological studies. More particularly, the present invention relates to a fiber optic pH probe in the form of a miniature pH sensor, constructed with the use of reversible dye indicators and single fiber optics, which is small enough to pass through a 22 gauge hypodermic needle and which can be implanted in tissue for physiological studies. The device is particularly well suited for use during exercise of the subject being studied.
A determination of pH is desirable in a wide variety of biological studies. In particular, for studies of blood oxygen content, pH is an important parameter for the oxygen-hemoglobin dissociation curve. For some diseases, e.g., sickle cell anemia, it is desirable to determine this curve in vivo during exercise.
Previous pH sensors have included sensors such as the glass electrode pH sensor built into a hypodermic needle as described by J. D. Czaban et al., Analytical Chemistry, 47, No. 11, 1787-92 (September 1975) and ibid., 48, No. 2, 277-81 (February 1976). While such electrodes are suitable for some purposes, their rigid needle construction is not desirable in certain physiological studies, such as exercise studies, because of irritation. Furthermore, such electrode systems have the inherent risk of electrical hazard.
Other devices for measuring pH are described, for example, in U.S. Pat. Nos. 4,033,330 and 4,041,932. Such prior art devices are designed to measure pH from outside the body and are not constructed so as to be easily implanted within the body.
By the present invention, there is provided an implantable pH measuring device which is of flexible construction and which can be placed in muscle or other tissue for in vitro or in vivo use without a needle remaining. The pH probe of the present invention is easily assembled, is potentially very low in cost and is thus capable of being readily manufactured in quantity for use as a disposable item. The present pH probe includes an ion permeable membrane envelope which encloses the ends of a pair of optical fibers. A pH sensitive dye indicator composition is present within the envelope. The probe operates on the concept of optically detecting the change in color of a pH sensitive dye.